Question

Make a poem about how will you explain how the Greeks knew that the earth is spherical?​

Answer 1

Objective

At the end of the lesson, you will be able to explain how the Greeks knew that the Earth is spherical.

The shape of the Earth is oblate spheroid. It has bulging equator and squeezed poles.

Have you ever wondered what the early philosophers thought about the shape of the Earth?

Learn about it!

• Around 500 B.C., most Greeks believed that the Earth was round, not flat. It was Pythagoras and his pupils who were first to propose a spherical Earth.
• In 500 to 430 B.C., Anaxagoras further supported Pythagoras' proposal through his observations of the shadows that the Earth cast on the Moon during a lunar eclipse.
• He observed that during a lunar eclipse, the Earth's shadow was reflected on the Moon's surface. The shadow reflected was circular.
• Around 340 B.C., Aristotle listed several arguments for a spherical Earth which included the positions of the North star, the shape of the Moon and the Sun, and the disappearance of the ships when they sail over the horizon.

North Star

• The North Star was believed to be at a fixed position in the sky. However, when the Greeks traveled to places nearer the equator, like Egypt, they noticed that the North Star is closer to the horizon.

The Shape of the Sun and the Moon

• Aristotle argued that if the Moon and the Sun were both spherical, then perhaps, the Earth was also spherical.

Disappearing Ships

• If the Earth was flat, then a ship traveling away from an observer should become smaller and smaller until it disappeared.
• However, the Greeks observed that the ship became smaller and then its hull disappeared first before the sail as if it was being enveloped by the water until it completely disappeared.

What is the shape of the shadow? How is the result of the experiment related to Aristotle's arguments about the shape of the Earth?

What could life on Earth be like if it is not a sphere?

Key Points

The following observations led the Greeks to conclude that the Earth is sphere:

• The Earth casts a circular shadow on the  Moon during a lunar eclipse.
• The North Star has different positions depending on the location of the observer.
• The Moon and the Sun are both spherical.
• A sailing ship becomes smaller and then its hull disappears first before the sail as if it is being enveloped by the water until it completely disappears.
• The angle of the Sun with the vertical direction at noon time during a summer solstice varies from place to place.

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Answer 2

Answer:

• This article discusses the history of the notion that the Earth is generally spherical. See Figure of the Earth for information on the geodetic Earth's dimensions and shape. See Earth's circumference for the measurement.
• This is about "Round world." See The World Is Round for more usages.
• A spherical Earth is depicted in mediaeval art, with sections for earth, air, and water (c. 1400)
• The idea of a spherical Earth first appears in writing in the fifth century BC, when Greek thinkers first brought it up. The nearly spherical shape of the Earth was established as a physical fact and its circumference was estimated by Hellenistic astronomy in the third century BC.
• During Late Antiquity and the Middle Ages, this knowledge progressively spread throughout the Old World.

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